This invention relates to a method for the adhesion of two ceramic articles to each other.
Recently, ceramics have come to attract special attention for their outstanding refractoriness. In consequence of the increasing adoption of ceramics in various industries, a great need is felt for the development of a reliable and simple method for joining two ceramic articles to each other or one ceramic article to an article of metallic material.
Various methods have heretofore been proposed for the adhesion of metallic materials to ceramic articles. Examples are the Telefunken method, activated metal method, hydrogen compound method, metal oxide method, powder compression method, hot press method, solder glass method, glaze and metal powder method, and copper oxide method. These methods, however, share a serious disadvantage in that their heating treatments must be performed either under a vacuum or in a reducing atmosphere.
Of the aforementioned methods, the solder glass method uses a soldering agent comprised of glass and an oxide and accomplishes the adhesion of a ceramic article to an article of metallic material by interposing the soldering material between the opposed surfaces of the two articles and heating the articles until their opposed surfaces are caused to adhere fast to each other by virtue of the fusion of the soldering material. According to this method, the heat treatment is generally carried out in the air at a relatively low temperature or in an inert gas or a vacuum at a high temperature. The use of an inert gas for high-temperature heat treatment is for the purpose of preventing the metallic material from oxidation. This method enjoys the advantage that the heat treatment can be effectively performed in the air when low temperatures suffice for the purpose of the treatment. However, since this method uses a low-melting PbO glass as one of the components of the soldering agent, the products joined by this method can endure heat up to 300.degree. to 400.degree. C. at most. Further, during the actual use of these products, the soldering materials exhibit poor chemical durability. When this method is effected by use of a soldering material containing a high-melting glass, the temperature of the heat treatment is inevitably elevated beyond 1000.degree. C. Consequently, the heat treatment must be carried out in a neutral gas or under a vacuum in order to preclude the possible oxidation of the metallic material.
One of the present inventors has proposed a method (Japanese Patent Publication No. 21569/1972) for applying a thin layer of silver to the surface of a ceramic article by the steps of coating the surface of the ceramic article with a mixture of copper with kaolin, heating the coated ceramic article in an oxidizing atmosphere kept at a temperature of not less than 900.degree. C. and, thereafter, spraying the hot surface of the ceramic article with silver carbonate while the article is kept heated at a temperature of not less than 700.degree. C. This method produces a thin layer of silver sticking with high adhesive strength to the surface of the ceramic article. In the case of a ceramic article of the nitride type, however; this method fails to provide reliable adhesion of the silver layer to the surface of the ceramic article. With a view to overcoming this weak point, the present inventors studied and tested this method elaborately. They have, consequently, developed and proposed a method (U.S. Pat. No. 4,163,074) which provides effective adhesion of metallic materials even to nitride type ceramic articles by causing the heat treatment which, in the aforementioned method, is performed in the oxidizing atmosphere to be carried out in a nitriding atmosphere instead.
The two methods of adhesion described above, however, are required each to give two heat treatments to each pair of articles being joined, with the heat treatments performed in special atmospheres. These methods permit adhesion of two ceramic articles to be effected by having the whole procedure carried through twice, i.e. once each for the two opposed surfaces of the articles. Thus, this adhesion necessitates a complicated operation.
An object of this invention is to provide a method for strongly joining two ceramic articles to each other by subjecting the articles to only one heat treatment performed in an oxidizing atmosphere, namely, in the air.